On the Menu: The problem with portion sizes

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How much should we eat? This seems like a simple question with a simple answer. But in a nation where two-thirds of adults are either overweight or obese better guidance is clearly needed.

One of the most common suggestions for losing weight or maintaining a healthful weight is to eat smaller portions. There are few nutritional concepts as vague, however, as "portion." How much a person should eat depends on so many factors -- how is anyone supposed to know whether three slices of pizza or a large bowl of salad is too small, too big or just right?

Knowing more about the nutritional content of different foods can help and many people use nutritional labels to make those purchasing decisions. In 2008, when the Food and Drug Administration conducted its most recent Health and Diet survey, 77 percent of consumers said that they consult a label the first time they buy a product. Unfortunately, FDA rules for determining and listing the serving size of products often lead to confusing and misleading information.

Last year, the Center for Science in the Public Interest, a nonprofit consumer watchdog agency, issued a report highlighting the worst serving-size offenders. Foods with the most misleading serving sizes included canned soups, ice cream and nonfat cooking sprays, many of which exploit legal loopholes to make their products appear more healthful than they are. One of the center's biggest concerns, said senior nutritionist Jayne Hurley, is that "the portion sizes we see on all food labels in the grocery store are mainly based on data of what people ate in the '70s."

Americans were slimmer then, and the amounts they reported eating in one sitting -- the definition of a serving -- seem unrealistically small today. How often does someone eat just 15 potato chips?

When serving sizes are unrealistic, foods may benefit from a kind of halo effect, Ms. Hurley said. After all, a "serving" of potato chips has just 160 calories, and that's not so bad. But what if the average consumer today eats 45 chips, for 480 calories? Confronted with that calorie count, more people might skip the potato chips.

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